/Engine/Source/Runtime/RenderCore/Public/RenderGraphDefinitions.h
Esoteric helper class which accumulates handles and will return a valid handle only if a single unique handle was added. Otherwise, it returns null until reset. This helper is chiefly used to track UAVs tagged as 'no UAV barrier'; such that a UAV barrier is issued only if a unique no-barrier UAV is used on a pass. Intended for internal use only.
template<typename HandleType> class TRDGHandleUniqueFilter